Tubular membrane separation apparatus end joint seal

ABSTRACT

The invention provides a tubular membrane separation apparatus useful for ultrafiltration and reverse osmosis. A tubular separation element (1) is fitted in a porous pressure-resistant tube (2) which is inserted in a liquid collector tube (3) of larger diameter. The collector tube (3) is detachably connected to connector tubes (6) by joints (4). Each end of the separation element (1) is held between the inner surface of the joint (4) and the end of the connector tube (6) and thereby sealed. The separation element (1) is replaceable, and the apparatus can be disassembled for cleaning.

TECHNICAL FIELD

This invention relates to a tubular membrane separation apparatus forthe ultrafiltration or reverse osmosis of solutions.

BACKGROUND ART

Various tubular membrane separation apparatus are already known. Many ofthese apparatuses are not provided with a liquid collector tube for theseparation element, or include a plurality of separation elements whichare housed in a single liquid collector tube. There are a few separationapparatuses in which each liquid collector tube houses a singleseparation element and the components are separable for cleaning and canbe reassembled. Published Examined Japanese patent application Sho No.52-37994 discloses a separation apparatus comprising a tubular supportmember having a large number of pores in its peripheral wall andaccommodating a tubular semipermeable membrane in its interior. Thisapparatus includes a gasket of special shape and involves the problem ofnecessitating a special tool and skill for the removal and installationof the tubular semipermeable membrane.

Other separation apparatuses also have problems. The semipermeablemembrane is inconvenient or costly to replace since the separationelement is joined to an expensive porous pressure-resistant tube. Whennot separable into individual parts, the apparatus can not be cleanedand is liable to have sanitation troubles. Gaskets of special shape, ifused for securing the liquid collector tube, support member andseparation element, render the apparatus costly.

DISCLOSURE OF INVENTION

According to this invention, a tubular separation element comprising aporous backing member and a semipermeable membrane formed over the innersurface of the member is fitted in a porous pressure-resistant tubewhich is inserted in a liquid collector tube having an inside diameterslightly larger than the outside diameter of the pressure-resistanttube. A joint member is detachably attached at its one end to each endof the collector tube as by screw-thread engagement therewith. The endof the porous pressure-resistant tube is held in contact with aninterior bearing face of the joint member. A narrow liquid passage isformed between the collector tube and the pressure-resistant tube. Thejoint member has an outlet bore through which the liquid passage is incommunication with the outside. The liquid filtered by the separationelement and flowing through the passage is run off via the outlet bore.

The separation element has a slightly enlarged open end within the jointmember. A connector tube extends into the joint member through the otherend thereof toward the enlarged end of the separation element and holdsthe enlarged end between the joint member and the forward end of theconnector tube to prevent the leakage of liquid.

Since the separation apparatus of this invention is assembled fromdetachable components, the apparatus can be assembled or disassembledwithout necessitating the use of any special tool or skill. Thesemipermeable membrane is replaceable merely by replacing the separationelement which is inexpensive. This is much more economical than thereplacement of the combination of the membrane and thepressure-resistant tube conventionally needed.

Additionally the separation element can be sealed by the joint memberand the connector tube which hold the enlarged end of the elementtherebetween, hence sanitary. Thus overcoming the problems encounteredwith the conventional tubular separation apparatus, the inventionassures various outstanding advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a tubular separation apparatusembodying the present invention;

FIG. 2 is a sectional view of a device for diametrically enlarging theend of a separation element to show how the end is enlarged;

FIGS. 3 and 4 are sectional views showing other embodiments of the meansfor holding the end of the separation element;

FIG. 5 is a sectional view showing another embodiment of the tubularseparation apparatus of this invention; and

FIG. 6 is a sectional view showing a further embodiment of thisinvention.

BEST MODE OF CARRYING OUT THE INVENTION

A tubular separation element 1 is fitted in a porous pressure resistanttube 2 which is inserted in a liquid collector tube 3. Six to fourteensuch collector tubes are parallelly arranged with their endsinterconnected by U-shaped connector tubes 6 to connect all theseparation elements 1 together in series.

The separation element 1 comprises a porous backing tube uniformlycoated with a semipermeable membrane over the inner surface. Theseparation element 1 can be produced by various known methods forexample, by the method disclosed by S. Loeb in Desalination, 1, 1966.

The separation element has at each end a diametrically enlarged flaredportion 11 to provide the seal structure to be described later. FIG. 2shows a device for forming the enlarged flared portion 11 at the end ofthe separation element 1. The device comprises a forming iron 21 havinga peripheral shape conforming to the shape of the enlarged flaredportion 11 and disposed upright in a cylindrical heater 22. Athermocouple 23 detects the temperature of the forming iron 21 tocontrol the heat generation of the heater 22 and maintain thetemperature at an optimum level suited to the material of the separationelement 1.

The end of the separation element 1 is fitted to and pressed against theforming iron 21 for several seconds, whereby the diametrically enlargedflared portion 11 can be formed. The shape, maximum length and maximumdiameter of the enlarged flared portion 11 are suitably determined inaccordance with the kind of the material of the separation element. Whenthe enlarged flared portion 11 has an outwardly spreading shape as shownin FIG. 1 for example, the portion 11 has an angle of inclination of 10°to 30° and a length of 4 to 10 mm. When the separation element has adiameter of about 1 inch, the enlarged portion has a maximum diameter of1.1 to 1.5 inches. If the separation element is made of a thermoplasticmaterial and is sufficiently stiff, the end of the separation elementcan be diametrically enlarged as desired by being pressed against theforming iron 21. The separation element 1 may be wet or dry when pressedagainst the forming iron 21, and there is no need to use any lubricant.

It is suitable that the forming iron 21 have a surface temperature whichis lower than the melting point of the material of the separationelement 1 but is higher than the softening point of the material. If thetemperature of the forming iron is higher than the melting point of thesemipermeable membrane material, the enlarged portion formed becomesharder and more susceptible to cracking. Precautions should therefore betaken to avoid such objection.

The enlarged flared portion 11 is formed in the following manner, forexample. When the separation element comprises a tube of porouspolyester nonwoven fabric coated over the inner surface with asemipermeable membrane of polysulfone resin (product of Union CarbideCorporation), the suitable temperature is in the range of 120° to 170°C. A satisfactory enlarged portion 11 can be formed by pressing the endof the separation element against the forming iron 21 for about 10seconds.

The porous pressure-resistant tube 2 is slightly shorter than the length(about 3 m) of the separation element 1 and has an inside diameterapproximately equal to the outside diameter of the separation element.The tube may have any of various known constructions. Examples of usefultubes are pipes made of metal or a thermoplastic resin selected frompolyethylene, polyvinyl chloride, polypropylene, polyester,polycarbonate and polyacetal which have a large number of pores in thewall thereof, or porous tubes produced by impregnating a tube of glassfiber fabric with phenolic resin and curing the resin as disclosed inPublished Examined Japanese patent application Sho No. 39-30143.

The collector tube 3 is shorter than the porous pressure-resistant tube2 and has an inside diameter slightly larger than the outside diameterof the porous pressure-resistant tube 2. When the pressure-resistanttube 2 is inserted into the collector tube 3, a narrow annular liquidpassage 5 is formed between the two tubes. The liquid passage 5 may havea very small width. When the pressure-resistant tube 2 has an outsidediameter of 1 inch, the collector tube 3 may have an inside diameterwhich is 0.5 mm larger to achieve the desired result. The collector tube3 has at each end a tapered threaded portion 7 for screw-threadengagement with a joint member 4. The pressure-resistant tube 2 and theseparation element 1 are fitted into one end of the joint member 4, andthe connector tube 6 is fitted into the other end thereof to hold theseparation element 1 in communication with the connector tube 6.

When the joint member is joined to the collector tube 3, the forward endof the pressure resistant tube 2 is fixedly fitted to a bearing face 14formed on the inside of the joint member 4 to provide a liquid passagebetween the outer periphery of the pressure-resistant tube 2 and theinner periphery of the joint member 4. The joint member is formed in aside portion thereof with an outlet bore 15 communicating with theliquid passage 5 within the joint for drawing off the filtrate flowingthrough the passage 5. The joint member 4 and the connector tube 6 canbe made from metal, but from the viewpoint of economy and ease ofmachining, it is preferable to make them from a thermoplastic resinselected from polyethylene, polypropylene, polyvinyl chloride,polystyrene, polycarbonate, polyacetal, etc.

The connector tube 6 has at its end a tapered face 12 having the sameinclination as the outwardly spreading enlarged flared portion 11 of theseparation element 1. The joint member 4 has inside thereof a taperedface 13 having the same inclination as, and corresponding to, thetapered face of the connector tube 6. When a cap nut 8 is fitted over anannular projection 10 on the outer periphery of the connector tube 6 andscrewed on screw threads 9 of the joint member 4, the tapered face 12 atthe forward end of the connector tube 6 and the tapered face 13 of thejoint member 4 firmly hold the enlarged flared portion 11 of theseparation element 1 therebetween to provide a seal. This mode ofconnection is called "sanitary connection" and is especially desirablefor devices for handling liquids, such as food and pharmaceuticalproducts, containing a component susceptible to spoiling or rotting.Although the sanitary connection usually does not require a gasket, itis preferable to cover the tapered portions 12 and 13 with a thin rubberring or like shock absorbing members 41 and 61 when a semipermeablemembrane of low strength must be used for the separation (FIG. 6).

FIG. 3 shows another example of sanitary connection. The connector tube6 has a vertical end face, and a holding ring 17 having a tapered faceis disposed at the tube end with a gasket 16 provided between the ringand the tube end.

FIG. 4 shows another example in which stepped holding faces 18 and 19are formed at the forward end of the connector tube 6 and on the innerside of the joint member 4 to hold the enlarged portion 11 of theseparation element 1 between the faces 18 and 19 for sealing.

FIG. 5 shows a joint member 4 provided in its inner surface with acircumferential flow passage 20 in the form of a deep groove andintersecting the outlet bore 15.

The liquid passing through the membrane flows through the passage 5 inthe collector tube 3 axially of the tube, reaches the joint member 4,then flows through the enlarged passage 20 circumferentially thereof andruns out from the outlet bore 15. Thus the filtrate can be drawn offfrom the tube smoothly.

The apparatus of this invention will be assembled usually in thefollowing manner. First, the porous pressure-resistant tube 2 is placedinto the liquid collector tube 3, and the joint members 4 are attachedto opposite ends of the collector tube 3. Next, one of the diametricallyenlarged flared portions 11 formed at opposite ends of the separationelement 1 is slightly deformed inward by pressing and pushed into thepressure-resistant tube 2 through one of the joint members. When theseparation element has been completely pushed in with the other end ofthe separation element reaching the tapered face 13 of the joint member4, both ends of the separation element 1 are on the tapered faces 13 ofboth joint members. The slightly inwardly deformed enlarged portion 11is then restored to the original outwardly spreading position bystroking with a finger inserted into the joint member 4 through itsopening. Finally the connector tubes 6 are inserted into the jointmembers, and the cap nuts 8 are fully tightened up to seal the enlargedportions 11, whereby the apparatus is completely assembled.

The separation element 1 can be withdrawn by a reverse procedure.

With the apparatus of this invention, the membrane can be replacedeasily and inexpensively. Without the gasket of special shapeconventionally used, the apparatus does not involve sanitation problems,while it is easy to clean because the parts are separable. Thus theapparatus is free of the problems conventionally experienced.

INDUSTRIAL APPLICABILITY

The tubular membrane separation apparatus of this invention is usefulfor the ultrafiltration and reverse osmosis of aqueous solutions ofhigh-molecular-weight materials and colloidal solutions for preparingfoods, drugs, coating compositions, etc.

We claim:
 1. A tubular membrane separation apparatus including aseparation element (1) having a tubular porous backing member with aninner surface and a semipermeable membrane formed over the inner surfaceof the backing member having an inside diameter, and a porouspressure-resistant tube (2) having the separation element (1) insertedtherein, the apparatus being characterized by a liquid collector tube(3) having an inside diameter slightly larger than the outside diameterof the pressure-resistant tube (2) and fitting around thepressure-resistant tube (2) to provide a narrow liquid passage (5)between the collector tube (3) and the pressure-resistant tube (2), apair of joint members (4) detachably attached at one end of each memberto each end of the collector tube (3) and supporting the end of thepressure-resistant tube (2), each joint member having an inner surfaceand being formed in a side portion thereof with an outlet bore (15)communicating with the liquid passage (5), the separation element (1)being detachably inserted into the pressure-resistant tube (2)projecting outwardly at its end from the end opening of thepressure-resistant tube (2) and being provided at its ends withdiametrically enlarged end portions (11) respectively disposed withinone of the joint members (4), a pair of connector tubes (6) inserted inthe joint members (4) at the other ends thereof and detachably joined tothe joint members (4), each connector tube (6) having an inside diameterapproximately equal to that of the semipermeable membrane and eachenlarged portion (11) of the separation element (1) being solelyfrustoconically tapered and spread outward toward its outer extremity,and the inner surface of each joint member (4) and the inserted end ofeach respective connector tube (6) being provided with frustoconicallytapered faces (12) and (13) having the same taper as each enlargedportion (11) of the separation element (1), the enlarged portions (11)of the separation element (1) being sealingly held against the taperedfaces (12) and (13) of the joint member (4) and the connector tube (6)at each end thereof.
 2. A tubular membrane separation apparatusincluding a separation element (1) having a tubular porous backingmember with an inner surface and a semipermeable membrane formed overthe inner surface of the backing member having an inside diameter, and aporous pressure-resistant tube (2) having the separation element (1)inserted therein, the apparatus being characterized by a liquidcollector tube (3) having an inside diameter slightly larger than theoutside diameter of the pressure-resistant tube (2) and fitting aroundthe pressure-resistant tube (2) to provide a narrow liquid passage (5)between the collector tube (3) and the pressure-resistant tube (2), apair of joint members (4) detachably attached at one end of each memberto each end of the collector tube (3) and supporting the end of thepressure-resistant tube (2), each joint member having an inner surfaceand being formed in a side portion thereof with an outlet bore (15)communicating with the liquid passage (5), the separation element (1)being detachably inserted into the pressure-resistant tube (2)projecting outwardly at its end from the end opening of thepressure-resistant tube (2) and being provided at its ends withdiametrically enlarged end portions (11) respectively disposed withinone of the joint members (4), a pair of connector tubes (6) inserted inthe joint members (4) at the other ends thereof and detachably joined tothe joint members (4), each connector tube (6) having an inside diameterapproximately equal to that of the semipermeable membrane and theenlarged portions (11) of the separation element (1) being tapered, anda holding ring (17) having an inside diameter approximately equal tothat of the semipermeable membrane and an outer peripheralfrustoconically tapered face inserted into each joint member (4) fromthe opening of the other end thereof, a gasket (16) being providedbetween each holding ring (17) and the inserted end of each connectortube (6), the enlarged portions (11) of the separation element (1) beingsealingly held against the holding ring (17) and a tapered face (13) ofthe joint member (4) at each end thereof.
 3. A tubular membraneseparation apparatus as defined in claim 1 wherein the inner surface ofeach joint member (4) and the inserted end of the connector tube (6) arecovered with a thin shock absorbing member to hold the enlarged portion(11) of the separation element (1) therebetween.
 4. A tubular membraneseparation apparatus as defined in claim 1 wherein the joint member (4)is formed in its inner surface with a deep circumferential flow passage(20) intersecting the outlet bore (15).
 5. A tubular membrane separationapparatus as defined in claim 1 wherein a cap nut (8) is fitted over anannular projection (10) on the outer periphery of an end portion of theconnector tube (6) and is detachably joined to a threaded face (9)formed on the outer periphery of an end portion of the joint member (4)to draw the connector tube (6) into the joint member (4) and hold theenlarged portion (11) of the separation element (1) between the innersurface of the joint member (4) and the connector tube (6).